The present invention relates to method and apparatus for winding successive convolutions of one or more continuous strands of material onto a workpiece. More particularly, it concerns an improved method and apparatus for successively winding multiple strands of wire about different angular sectors of ring-shaped articles such as toroidal cores, the different sectors being wound in different directions.
As used herein, the term "core" means a ring-shaped article having the plane closed curve cross section of a toroid, or any one of various other different cross sections. The term "wire" as used herein means any material in the form of a flexible strand which is not so supple that it buckles easily when pushed from one end in a length-wise direction. The terms "continuous wire supply" and "continuous wire source" mean that the length of continuous wire in the supply coil or source is sufficiently long to enable a plurality of cores to be wound from the supply or source before the wire is used up. As used herein, the term "oval-shaped" refers to a closed curve having opposite ends with different radius of curvature.
Wire wound ferrite cores have been used as electronic components for many years. They are particularly adapted for producing a gapless magnetic field. Inductance coils and transformers can be constructed in this manner. Rheostats can be constructed with cores wound with resistance wire. Very small wire wound cores have also been used as memory elements in computers.
Heretofore, the wire has often been wound onto such cores by hand. This process is time consuming and tedious and frequently results in inferior coils due to non-uniform spacing of the wire turns around the core. More recently, the wire has been wound onto such cores through the use of a rotating winding ring or shuttle which carries several loops of wire and rotates at high speed through the central aperture of the core. U.S. Pat. No. 2,810,530 discloses an exemplary apparatus for winding cores in this manner. Such apparatus require the constant attention of an operator who must mount each core, manually wind the appropriate number of loops of wire about the shuttle, and remove the core from the shuttle upon the completion of the winding operation.
Improved winding apparatus have been developed which do not require the insertion of a winding ring or shuttle, or any other element through the central aperture of the core. Instead, a coil of wire is formed which extends through the central aperture of the core. Individual turns about the core are made from the loops of the coil during continuous rotation of the coil. One such apparatus is disclosed in U.S. Pat. No. 3,132,816. In that apparatus, loops of wire are held frictionally between the engaging faces of two ring-like belts which are rotatably driven about their central axes. The wire loops pass through the center of a core supported between separated portions of the belts. The trailing end of the wire is rigidly held so that as the coil rotates the wire loops are wound into turns about the core.
U.S. Pat. No. 3,985,310, owned by the assignee of the present application, discloses a shuttleless core winding apparatus in which a length of wire is fed into a radially inwardly facing annular channel through a curved feeding tube. The wire is propelled about the channel by two pairs of driven pinch rollers to form a number of radially spaced circular loops. The upper and lower boundaries of the channel maintain the loops in a single concentric layer. A gap is provided in the channel for receiving the core so that as each circular loop is formed, the wire in that loop passes through the core opening. When enough wire has been fed, the trailing end of the wire is held. The circulation of the loops through the core opening continues and each loop is shrunk into turns about the core, one new turn being completed for each circulation of the loops about the annular channel. The winding of two or more wires simultaneously around the core (known as bifilar and multi-filar winding) can be accomplished by the apparatus of U.S. Pat. No. 3,985,310.
The apparatus of U.S. Pat. No. 3,985,310 has certain limitations. Because the wire loops are formed into a single concentric layer within the circular channel, provisions must be made to ensure that each loop is driven around the channel at an angular velocity which is equal to or greater than that of any loop radially outwardly of it. If the angular velocity of any inner loop is less than that of any outer loop, the inner loops circulate around the channel more slowly and get larger and jam against the outer loops, preventing proper winding of the core. To avoid this result, the driven pinch rollers are not cylindrical but instead are beveled and supported at an angle to each other. Roller wear and inprecise positioning of the rollers can result in an improper speed relationship between the concentric wire loops, and this will often terminate the winding operation.
Furthermore, the loop capacity of the apparatus of U.S. Pat. No. 3,985,310 is relatively small and this places an upper limit on the number of turns that can be wound around the core. If too many loops are formed within the channel of the apparatus, it is difficult to maintain the required radial speed relationship. This often results in jamming or buckling of the loops. The opposing pairs of driven pinch rollers are not well suited for providing sufficient positive driving force to enable heavier gauge wire to be wound around larger cores. Winding with heavier wire also requires positive guidance of the wire on both its inner and outer boundaries as the loops are formed and circulated. The apparatus of U.S. Pat. No. 3,985,310 has no inner boundary guidance.
Many of the shortcomings of the aforementioned prior art devices were overcome by the apparatus disclosed in U.S. Pat. No. 4,288,041, also owned by the assignee of the present application. That patent discloses a shuttleless toroidal core winder apparatus which includes a U-shaped wire receiving channel having a semi-circular portion with a gap and a pair of openended legs. The ends of the channel legs are positioned adjacent opposite sides of a rotatably mounted drum which is driven by a resilient endless belt engaging approximately one-half of its annular outer surface.
In the device of U.S. Pat. No. 4,288,041, a toroidal core is supplied and rigidly supported in the gap by a core feeding mechanism. A grooved gap crosser is thereafter extended through the central opening of the core to bridge the gap and complete the channel. A pair of pinch roller type feed/brake mechanisms propel and guide the leading ends of the wires into the channel, through the core opening, and up one channel leg to the drum. There the wires are frictionally held between the drum and the belt and they are positively driven into the other channel leg, through the core opening, and back to the drum. Continued feeding of the wire results in the formation of a coil having a plurality of vertically stacked loops which extend through the core opening and are alternatively made of different ones of the wires. Thereafter, staggered braking of the trailing ends of the wires causes the loops to be successively peeled radially inwardly from the channel and the drum as the coil is continuously circulated. The loops are shrunk and tightened into turns about the core as it is slowly rotated about its axis by the core feeding mechanism. First and second shear mechanisms cut off the trailing and leading ends of the wires at the beginning and end of the winding operation, respectively.
The apparatus of U.S. Pat. No. 4,288,041 has been used commercially on an extensive basis with a high degree of reliability at a high rate of production. However, it is only capable of winding one or more strands of wire in one direction about one angular sector (portion of the circumference) of a toroidal core such as illustrated in FIG. 4 herein. In the field of electronics, there are many uses for a ferrite core having two wire windings on different angular sectors of the core, the windings being in opposite direction or sense. In other words, one winding on one sector of the core is wound in a reverse direction with reference to a second winding on another sector of the core. This type of winding is referred to herein as "multiple reverse sector winding", an example of which is illustrated in FIG. 5 herein. None of the aforementioned prior art apparatus is capable of winding toroidal cores in this fashion, including U.S. Pat. No. 4,288,041.